Development of the face is a complex, multi-step process involving multiple genes, signaling pathways, and cellular behaviors. Disruption of any of these steps can lead to craniofacial malformations including cleft lip and cleft palate, common birth defects in humans. The transcription factor serum response factor (SRF) is an important regulator of craniofacial morphogenesis. This is evidenced by conditional deletion of Srf in the mouse craniofacial mesenchyme which causes a broad spectrum defects including cleft face and mandibular aplasia. Interestingly, SRF can be activated by multiple signaling pathways that themselves are required for craniofacial development and also associated with human cleft lip and/or palate. These include the platelet-derived growth factor (PDGF) receptor pathway and the fibroblast growth factor (FGF) receptor pathway. Recent work in the Soriano laboratory has suggested that activation of the PDGF receptor and FGF receptor pathways mobilizes distinct sets of SRF cofactors, the ternary complex factors (TCFs) and myocardin related transcription factors (MRTFs), and thereby alters the set of SRF-induced genes. This represents an attractive model for how different signaling molecules can direct specific responses through a shared transcription factor. This model has not yet been tested in vivo and the relative contribution of the SRF-MRTF complex and the SRF-TCF complex to craniofacial development is completely unknown. Also mysterious is how SRF-directed gene expression leads to specific cellular behaviors and how such behaviors are altered in cleft lip and palate. This proposal will address these questions using two complementary approaches. First, I will develop a novel mouse model which expresses a form of SRF in the craniofacial mesenchyme incapable of binding MRTFs, but retaining TCF binding activity. I will use this mouse model to determine the cellular behaviors and morphological outcomes attributable to SRF-TCF and SRF-MRTF during craniofacial development. Second, I will stimulate primary palatal mesenchyme cells with PDGF-AA and FGF-1 and assess the differential distribution of SRF throughout the genome by chromatin immunoprecipation and high-throughput sequencing. Secondary analysis of these gene sets will inform how SRF-mediated transcription coordinates the cellular behaviors required for proper craniofacial development. These inventive studies will allow dissection of the function of specific SRF-cofactor complexes for the first time in vivo and link our understanding from signaling to transcriptional regulation to cellular behaviors and finally morphogenesis. The proposed research strategy takes advantage of the expertise and many mouse and technical resources available in the laboratory in order to better understand the intricate nature of craniofacial development and ultimately lead to new therapeutic approaches to treating human disease.
Serum Response Factor (SRF) is a transcription factor that regulates a variety of processes in multiple tissues, both during development and adult life, and aberrant SRF activity has been associated with several types of cancer and metastasis. Defects in craniofacial development are a common birth defect in humans, with cleft lip and/or palate affecting approximately 1 in 700 births. The SRF studies in this proposal will increase our understanding of how signaling pathways activate specific transcriptional responses during craniofacial development and how defects in these processes lead to birth defects such as cleft lip and palate, supporting the development of novel therapeutic approaches.